Expansion bullet for heat exchanger tube

ABSTRACT

An expansion bullet for a heat exchanger tube includes a leading edge face, a trailing edge face, and a bullet body insertable into a tube of a heat exchanger to expand the tube. The bullet body extends from the leading edge face to the trailing edge face and has an outer profile defined by a single radius. An expansion mechanism for a tube of heat exchanger includes a bullet driving device and an expansion bullet drivable by the bullet driving device. The expansion bullet includes a leading edge face, a trailing edge face, and a bullet body insertable into a tube of a heat exchanger to expand the tube. The bullet body extends from the leading edge face to the trailing edge face and has an outer profile defined by a single radius.

BACKGROUND OF THE INVENTION

The subject matter disclosed herein relates to heat exchanger tubes.More specifically, the subject disclosure relates to expansion bulletsfor manufacturing heat exchanger tubes.

Heat exchangers of, for example, air conditioners, include a pluralityof heat exchanger fins and a plurality of heat exchanger tubes. Thetubes are passed through holes in the fins, then are expanded to forcethe tubes into interference fit with the fins, thereby securing thetubes in place relative to the fins. Typically, the tubes are expandedvia a bullet having a maximum diameter the same as that of the desiredfinal inner diameter of the tube. The bullet 100, an example of which isshown in FIG. 3, is fixed to a mandrel for inserting into the tube, andtypically has a radiused leading edge 102 and a conical or cylindricalbody 104. The typical cross-sectional shape of an expansion bulletrequires application of a high force in order for the bullet tosuccessfully expand the tube. Further, especially when expandingaluminum tubes, aluminum material builds up on the bullet, resulting ingalling and further increase in the necessary applied force.

BRIEF DESCRIPTION OF THE INVENTION

According to one aspect of the invention, an expansion bullet for a heatexchanger tube includes a leading edge face, a trailing edge face, and abullet body insertable into a tube of a heat exchanger to expand thetube. The bullet body extends from the leading edge face to the trailingedge face and has an outer profile defined by a single radius.

According to another aspect of the invention, an expansion mechanism fora tube of heat exchanger includes a bullet driving device and anexpansion bullet driveable by the bullet driving device. The expansionbullet includes a leading edge face, a trailing edge face, and a bulletbody insertable into a tube of a heat exchanger to expand the tube. Thebullet body extends from the leading edge face to the trailing edge faceand has an outer profile defined by a single radius.

These and other advantages and features will become more apparent fromthe following description taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter, which is regarded as the invention, is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other features, and advantages ofthe invention are apparent from the following detailed description takenin conjunction with the accompanying drawings in which:

FIG. 1 is a cross-sectional view of an embodiment of a tube expansionbullet;

FIG. 2 is another cross-sectional view of an embodiment of an expansionbullet; and

FIG. 3 is a cross-sectional view of a typical expansion bullet.

The detailed description explains embodiments of the invention, togetherwith advantages and features, by way of example with reference to thedrawings.

DETAILED DESCRIPTION OF THE INVENTION

Shown in FIG. 1 is a schematic of an expansion mechanism 10 for a tube12 of, for example, a heat exchanger. The illustrated tube 12 is formedof an aluminum material, but other materials, for example, copper, maybe utilized. The mechanism 10 includes a mandrel 14 which supports anexpansion bullet 16. The expansion bullet 16 has a maximum diameter 18greater than an unexpanded diameter 20 of the tube 12. The mandrel 14and bullet 16 are driven into the tube 12 to expand the tube 12 to aninner diameter substantially equal to the maximum diameter 18 of thebullet 16. Though, expansion utilizing a mandrel 14 to drive the bullet16 is shown in FIG. 1 and described herein, it is merely exemplary. Itis to be appreciated that other bullet 16 driving means, such as a fluidapplied to the bullet 16, are contemplated within the present scope.

To reduce the force necessary to expand the tube 12 to the desireddiameter, the bullet 16 has a specific cross-sectional shape, as shownin FIG. 2. The bullet 16 is substantially symmetrical about a bulletaxis 22 extending along a length 24 of the bullet 16. The bullet 16 hasan inner diameter 26 defining a bullet opening 28 for mounting thebullet on the mandrel 14. The bullet has a leading edge face 30 and atrailing edge face 32 which are substantially planar and perpendicularto the bullet axis 22, and a bullet body 34 extending the length of thebullet 16 between the leading edge face 30 and the trailing edge face32. A surface profile of the bullet body 34 is a single continuousradius 36. While a single continuous radius is shown in FIG. 2, it is tobe appreciated that other configurations to reduce friction may beutilized. For example, the radius 36 may be interrupted along its lengthby on or more chamfers or steps.

A center point 38 of the continuous radius 36 is shown in FIG. 2. Insome embodiments, an axial position of the center point 38 is biasedtoward the trailing edge face 32 such that, a leading edge face diameter40 is less than a trailing edge face diameter 42. In some embodiments,the center point 38 is located along the length of the bullet 16 betweenabout ¼ and ⅓ of the distance from the trailing edge face 32 to theleading edge face 30. Further, in some embodiments, the center point 38is offset radially from the bullet axis 22. For example, as shown inFIG. 2, the center point 38 may be located outside of the bullet 16.

By way of example, a bullet 16 utilized to expand a tube 12 having abouta ⅜″ outer diameter 44 is shown in FIG. 2. For such a bullet 16, theleading edge face diameter 40 is about 0.188 inches and the trailingedge diameter 42 is about 0.321 inches. The continuous radius 36 of thebullet 16 is about 0.350 inches. The continuous radius 36 issubstantially proportional to the outer diameter 44 (shown in FIG. 1) ofthe tube 12 to be expanded. For larger outer diameters 44 a largerradius 36 is utilized, while for a smaller outer diameter 44, a bullet16 having a smaller radius 36 is utilized.

In some embodiments, the bullet opening 28 is chamfered at the leadingedge face 30 and the trailing edge face 32 to ease installation of thebullet 16 on the mandrel 14.

In some embodiments, the bullet 16 is formed from a steel material, forexample, tool steel. It is to be appreciated, however, that othersuitable materials may be utilized and are contemplated within thepresent scope. To decrease buildup of aluminum material on the bullet 16during use, and thus reduce galling between the bullet 16 and the tube12, the bullet 16 may include a coating material applied to the bullet16. This coating may be, for example, a metallic coating, a plasticcoating, a nano coating, and/or a surface treatment, or the like toreduce friction and galling, add wear resistance, and/or increasecorrosion resistance. In some embodiments, the coating is a hard chromeplating.

While the invention has been described in detail in connection with onlya limited number of embodiments, it should be readily understood thatthe invention is not limited to such disclosed embodiments. Rather, theinvention can be modified to incorporate any number of variations,alterations, substitutions or equivalent arrangements not heretoforedescribed, but which are commensurate with the spirit and scope of theinvention. Additionally, while various embodiments of the invention havebeen described, it is to be understood that aspects of the invention mayinclude only some of the described embodiments. Accordingly, theinvention is not to be seen as limited by the foregoing description, butis only limited by the scope of the appended claims.

1. An expansion bullet for a heat exchanger tube comprising: a leadingedge face; a trailing edge face; and a bullet body insertable into atube of a heat exchanger to expand the tube, the bullet body extendingfrom the leading edge face to the trailing edge face, the bullet bodyhaving an outer profile defined by a single radius.
 2. The expansionbullet of claim 1, wherein the single radius is substantially continuousand unbroken from the leading edge face to the trailing edge face. 3.The expansion bullet of claim 1, wherein a center point of the singleradius is axially offset along a length of the expansion bullet.
 4. Theexpansion bullet of claim 3, wherein the center point is axially offsetsuch that a leading edge face diameter is smaller than a trailing edgeface diameter.
 5. The expansion bullet of claim 1, wherein the leadingedge face and/or the trailing edge face are substantiallyaxially-oriented planar faces.
 6. The expansion bullet of claim 1,wherein a center point of the single continuous radius is radiallyoffset from a central axis of the expansion bullet.
 7. The expansionbullet of claim 6, wherein the center point is offset such that thecenter point is located outside of the expansion bullet.
 8. Theexpansion bullet of claim 1, further comprising a coating applied to theexpansion bullet.
 9. The expansion bullet of claim 8, wherein thecoating is one or more of a metallic coating, a plastic coating, a nanocoating, or a surface treatment to reduce friction.
 10. The expansionbullet of claim 1, further comprising a bullet opening to secure theexpansion bullet to a mandrel.
 11. An expansion mechanism for a tube ofheat exchanger comprising: a bullet driving device; and an expansionbullet configured to be driven by the bullet driving device: a leadingedge face; a trailing edge face; and a bullet body insertable into atube of heat exchanger to expand the tube, the bullet body extendingfrom the leading edge face to the trailing edge face, the bullet bodyhaving an outer profile defined by a single radius.
 12. The expansionmechanism of claim 11, wherein the single radius is substantiallycontinuous and unbroken from the leading edge face to the trailing edgeface.
 13. The expansion mechanism of claim 11, wherein a center point ofthe single continuous radius is axially offset along a length of theexpansion bullet.
 14. The expansion mechanism of claim 13, wherein thecenter point is axially offset such that a leading edge face diameter issmaller than a trailing edge face diameter.
 15. The expansion mechanismof claim 11, wherein the leading edge face and/or the trailing edge faceare substantially axially-oriented planar faces.
 16. The expansionmechanism of claim 11, wherein a center point of the single continuousradius is radially offset from a central axis of the expansion bullet.17. The expansion mechanism of claim 16, wherein the center point isoffset such that the center point is located outside of the expansionbullet.
 18. The expansion mechanism of claim 11, further comprising acoating applied to the expansion bullet.
 19. The expansion mechanism ofclaim 18, wherein the coating is one or more of a metallic coating, aplastic coating, a nano coating, or a surface treatment to reducefriction.
 20. The expansion mechanism of claim 11, wherein the bulletdriving device is a mandrel to which the bullet is secured.